As the son of two doctors, Ahmad grew up dreaming of being an emergency-room physician. With one year left before graduating medical school, the 23-year-old’s dream has turned to a nightmare: His E.R. over the past week has been the small rural house near Damascus where he and his friends stitch up wounded civilians and fighters, scraping by with no general anesthetics and tiny rations of antibiotics. And they work in constant terror of being jailed for their clandestine trauma surgery, or being killed in an attack. “We are working day and night,” Ahmad — not his real name — told TIME this week week from a Damascus suburb. “You cannot imagine what we have seen and done. There is no equipment to do things for people. We bring empty bags and ask people please to give us blood. But the rate of injuries is so high.”

The past month has been the deadliest yet in Syria‘s 18-month crisis, as the battle for Aleppo rages on. Forces loyal to President Bashar al-Assad have unleashed attack on rebel-held areas in Syria’s cities, hugely increasing the risk to the civilian population. About 226 people were killed on Monday alone, according to the pro-opposition Syrian Observatory for Human Rights, which estimates that as many as 21,000 people might have been killed since the conflict began But few have even attempted to count the wounded, whose scars will be born long after peace is finally restored.

Caring for the wounded is a massive challenge for those fighting the regime, with the regime working to stymie the efforts of aid organizations to send medical help. Assad’s security forces are also accused of targeting medics since the start of the conflict in early 2011, making it extraordinarily dangerous for young medics like Ahmad to continue for months to treat the wounded.

Organizations working in Syria estimate at least 60 medical personnel have been killed, and that hundreds more have been jailed for their work. “It is one of the first times in history in which medical staff are so systematically targeted,” says Patrick Villedieu, Deputy Director of International Operations for the Paris-based Doctors of the World, which treats Syrians in refugee camps in Lebanon and Jordan, since it is banned from operating in regime-held Syria, and regards the rebel areas as too dangerous. “We could save a lot of lives if we could work inside Syria,” Villedieu told TIME on Tuesday. “It’s much more dangerous now to smuggle medicines into Syria than to smuggle in weapons.”

That has left medical students like Ahmad — whose university studies have been halted by the conflict — to act as full-fledged triage units in one of the world’s bloodiest conflicts. In recounting his harrowing days treating wounded Syrians, Ahmad says he and his friends have had to improvise at short notice, making split-second decisions about how to save people’s lives with little equipment at hand, and no safe way to acquire it.

One night last week, Ahmad says, 17 people were wounded in heavy fighting in a village near Damascus, and rushed into the room where he, two other students, and two doctors sat waiting. “These people had shrapnel in them, they were hit by tanks and rockets, and four of them by snipers,” Ahmad says. “We had no chest tubes. So we made them from a serum bag and a tube.” When dawn broke, they ventured out to find antibiotics and chest tubes, returning in time to save the patients. But the outcome was far less certain during those first precious hours after the attack, when they were short of both drugs and chest bags. “If you don’t bring them fast, maybe the patient will die of septic shock,” he says.

In fact, hundreds, perhaps thousands, of Syrians have likely died from lack of treatment, according to organizations operating in the region. Avaaz, the activist organization based in New York, has smuggled in thousands of medical kits to opposition groups in Syria since the conflict began. But it believes the death toll would be markedly lower if there had been open supply lines for medicines and clinical equipment, and if medical personnel were allowed to work unimpeded. “These triage surgeons are being shelled, they are under continuous threats,” says Wissam Tarif, Avaaz’s Middle East Director in Beirut. “We have seen so many time doctors abandoning these makeshift hospitals, having to flee. This is war surgery under the harshest of circumstances.”

Ahmad says he has seen heart-breaking incidents caused by the dire lack of specialist doctors in rebel-held territory. He says many amputations have been carried out without general anesthetics and that many of those amputations might not have been performed at all, had more sophisticated operations been possible. “Some [patients] had big injuries in his leg or hand and his arteries are cut,” Ahmad says, in imperfect English. “We need a surgeon for vessels, but those are so, so, so few. So nobody can do anything for the patient except this [amputation].” The amputations are often performed under grueling conditions, “especially lack of blood bags,” Ahmad says. “Some patients die by pain and shock.”

With the conflict dragging into its 18th month, even Syria’s government-run health system is nearing collapse in many areas. In a grim briefing in Geneva on Tuesday, World Health Organization spokesman Tarik Jasarevic said there were critical shortages of medicines even in areas of Syria controlled by Assad’s regime. One reason is that Syria’s pharmaceutical factories — which had fulfilled about 90% of the country’s needs until the conflict began — have closed, unable to afford the rocketing price of fuel, or because many staff members have fled, or simply cannot reach their workplace anymore. Meanwhile, hundreds of doctors and nurses have abandoned their jobs in government hospitals around Aleppo, Damascus and Homs, as they flee the war zones. “The health facilities that have stopped functioning are located in the most affected areas, where the urgent need for medical and surgical interventions is the most prominent,” Jasarevic said in an email to TIME on Tuesday.

Ahmad still dreams of working in one of those government hospitals, but he senses it will be a long time before that happens. “I hope we can be back after a year,” he says. “But I am not sure.”

Until then, he remains determined to keep working as an underground medic despite the risks. One friend was arrested last September while carrying medicines to a makeshift clinic, he says. The young man has not been seen since. “I know what will happen if they find me,” Ahmad says. “But we have no choice, this is our work. We cannot leave. We cannot escape. If we don’t treat people, they will bleed to death.”